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3 ORBSCAN SYSTEM Use the principle of projectionForty scanning slit beams (20 from the left and 20 from the right with up to 240 data points per slit ) to scan the cornea and measure independently the X,Y & Z locations

4 Orbscan imagingForty slit images are acquired in two 0.7 second periodsEach of the 40 slit images triangulates one slice of ocular surfaceDistance between data slices average 250 microns

9 Elevation Orbscan measure elevationElevation is important the only complete scaler measure of surface shapeBoth slope & curvature can be mathematically derived from a single elevation map

10 BEST FIT SPHERE (BFS)The computer calculates a hypothetical sphere that matches as close as possible to the actual corneal shape being measuredCompares the real surface to the hypothetical sphere showing areas above the surface of the sphere in warm colours and areas below the surface in cool colours

17 AXIAL MAPProvides detailed keratometric information across the diameter of the corneaK readings are between certain values the cornea must be neither too steep nor too flat

18 AXIAL MAPTo create a good quality corneal flap in LASIK if either extremes (too steep or too flat) is the case, this can lead to surgical flap complicationsK readings of more than 48 D are an indication of potential keratoconus

23 PACHYMETRY MAPThe orbscan measures thickness from the tear film layer to descemet’s membrane and is thicker than that obtained with ultrasoundAdjustment factor (acoustic factor) ,the default setting is 92%Provides a reading showing the thinnest point of the cornea that may not necessarily be the central reading

25 PACHYMETRY MAP Thinnest point <470 micronIn pathological corneas, thinnest point is often displaced inferotemporalDifference of >100 microns from the thinnest point to the values at 7mm optical zone

33 POWER MAP Mean corneal power >45DIn addition to steep corneal curvatures-the bowtie or broken bowtie appearance indicative of early keratoconusCentral corneal asymetry a change within central 3mm optical zone of the cornea of more than 3D

34 Irregularity in central corneaGreater than 1.5 D in 3 mm zone andgreater than 2.0 D in 5 mm zone is considered abnormal and cause for concern

35 POSTERIOR ELEVATION MAPMany surgeons think the first sign of keratoconus appears on the posterior surface of the cornea3.13% of population screened for laser surgery had posterior ectasia criteria by orbscan , despite having axial topography classified as normal

39 Posterior elevation mapThe location of the steepest part of the posterior float should be relatively central , but is a more concern it be located away from the center and in an area of corneal thinningPosterior float difference;40 to 50 microns seems to be the maximum difference

41 Correlation of signs of the highest pointHighest point on the posterior elevation coincides with the highest point of anterior elevation , the thinnest on pachymetry and the point of steepest curvature on the power map

50 Composite/integrated informationSimilarly between anterior & posterior profiles a forward bending of areas shown above the BFS and association with the thinnest point on the corneaInferotemporal displacement of the highest point